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Rural Canada Geese Had More Distinct Bacterial DNA Variants Than Urban Birds

Canada geese and goslings at Lake Arlington in Arlington Heights, Illinois
Research · Disease, parasites & microbiology

Wild Canada geese (Branta canadensis) from rural parts of Illinois, USA had more distinct bacterial DNA variants in cloacal samples than birds from urban settings, according to a study published on 17 June 2026. The cloaca is the common opening of the digestive, urinary and reproductive tracts in birds, so a swab samples microbes associated with this body opening rather than only the intestine. Researchers sampled 106 geese in eight Illinois counties during June–August 2022 and compared bacterial communities with habitat, age and sex.

Sampling took place during the state’s annual goose-banding programme. Sites were classified using human population density and the proportion of impervious surfaces: urban sites averaged 480 people per square kilometre and 50% impervious cover, while rural sites averaged ten people per square kilometre and 3% impervious cover.

Rural birds had higher bacterial richness

The team sequenced the V4 region of the bacterial 16S rRNA gene, which identifies bacterial DNA signatures but does not show whether the organisms were alive, established in the bird or capable of causing disease. An ASV is a distinct 16S DNA sequence variant used as a fine-scale marker of bacterial diversity. Rural samples averaged about 215 observed ASVs compared with about 168 in urban samples. Broader phylogenetic diversity, which measures how evolutionarily different the detected bacterial lineages are from one another, did not differ. The rural samples therefore contained more detected sequence variants, but not a wider evolutionary spread of bacterial lineages.

Community composition also varied. Host age had the strongest and most consistent association: juveniles and adults differed in all of the study’s statistical approaches. Human population density showed a weaker association that was supported in two of three analytical approaches, while sex had little relationship with bacterial composition. The samples contained both gut-associated bacteria and lineages commonly associated with plants, soil and water, consistent with the ecology of grazing geese.

The study did not measure disease risk

DNA from bacterial groups that can include opportunistic pathogens occurred at low levels, but the sequencing method could not determine strain, virulence or viability. The authors therefore caution against interpreting these detections as evidence that the birds were infected or posed a public-health threat.

The measured effects were also small. Human population density explained about 1.5% of phylogenetic community variation and age about 2.6%, while diet, waterways, geography and other unmeasured factors may account for much more. Birds from the same sites may not have been fully independent samples, so the findings should not automatically be extended beyond the sampled Illinois populations.

The study provides a baseline showing that urban and rural Canada geese can differ in bacterial richness and community composition without demonstrating a difference in health. Repeated sampling across independent sites and seasons would be needed to identify the causes of those differences and determine whether any detected microbes have consequences for birds, other animals or people.

Sources and image credit

  1. Raudabaugh, D. B., Perez-Girones, S. V., Rivera, N. A., Latif, T., London, E. W., Pietrunti, N. F., Brown, W. M., Mateus-Pinilla, N. E., & Fournier, A. M. V. (2026). Variation in cloacal microbiota of Canada goose (Branta canadensis) across rural and urban areas in Illinois, USA. Frontiers in Microbiomes, 5, 1820309. https://doi.org/10.3389/frmbi.2026.1820309Primary peer-reviewed study. Cloacal swabs from 106 wild Canada geese in eight Illinois counties were analysed using 16S rRNA V4 sequencing. Rural birds had higher observed ASV richness; host age showed the strongest association with bacterial community composition, with a weaker association with human population density.

Image: OhanaSurf / Wikimedia Commons — Canada geese (Branta canadensis), including adults and goslings, at Lake Arlington in Arlington Heights, Illinois, USA, 17 May 2016. Representative image for this story; not presented as an animal or scene from the reported study or event. · CC BY-SA 4.0 · Source

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